Transistor laser optical switching and memory techniques and devices
A ring cavity light-emitting transistor device, including: a planar semiconductor structure of a semiconductor base layer of a first conductivity type between semiconductor collector and emitter layers of a second conductivity type; base, collector, and emitter metalizations respectively coupled with the base layer, said collector layer, and said emitter layer, the base metalization including at least one annular ring coupled with a surface of the base layer; and an annular ring-shaped optical resonator in a region of the semiconductor structure generally including the interface of the base and emitter regions; whereby application of electrical signals with respect to the base, collector, and emitter metalizations causes light emission in the base layer that propagates in the ring-shaped optical resonator cavity.
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This is a continuation of, and priority is claimed from, copending International Patent Application Number PCT/US2013/073414, filed Dec. 5, 2013, which, in turn, claims priority from U.S. Provisional Patent Application No. 61/797,427, filed Dec. 6, 2012, and said International Patent Application and U.S. Provisional Patent Application are incorporated herein by reference.
FIELD OF THE INVENTIONThis invention relates to semiconductor light emitting and lasing devices and techniques and, more particularly, to ring light-emitting transistors and transistor lasers, coherent field switching, and optical memory techniques and devices.
BACKGROUND OF THE INVENTIONIncluded in the background of the present invention are technologies relating to heterojunction bipolar transistors (HBTs, which are electrical tilted charge devices) and light-emitting transistors, transistor lasers, and tilted charge light-emitting diodes (respectively, LETs, TLs, and TCLEDs, all of which are optical tilted charge devices). A tilted charge device gets its name from the energy diagram characteristic in the device's base region, which has, approximately, a descending ramp shape from the emitter interface to the collector (or drain, for a two terminal device) interface. This represents a tilted charge population of carriers that are in dynamic flow—“fast” carriers recombine, and “slow” carriers exit via the collector (or drain).
Regarding optical tilted charge devices and techniques, which typically employ one or more quantum size regions in the device's base region, reference can be made, for example, to U.S. Pat. Nos. 7,091,082, 7,286,583, 7,354,780, 7,535,034, 7,693,195, 7,696,536, 7,711,015, 7,813,396, 7,888,199, 7,888,625, 7,953,133, 7,998,807, 8,005,124, 8,179,937, 8,179,939, 8,494,375, and 8,509,274; U.S. Patent Application Publication Numbers US2005/0040432, US2005/0054172, US2008/0240173, US2009/0134939, US2010/0034228, US2010/0202483, US2010/0202484, US2010/0272140, US2010/0289427, US2011/0150487, and US2012/0068151; and to PCT International Patent Publication Numbers WO/2005/020287 and WO/2006/093883 as well as to the publications referenced in U.S. Patent Application Publication Number US2012/0068151.
An optical tilted charge device includes an active region with built-in free majority carriers of one polarity. At one input to this active region, a single species of minority carriers of opposite polarity are injected and allowed to diffuse across the active region. This active region has features that enable and enhance the conduction of majority carriers and the radiative recombination of minority carriers. On the output side of the region, minority carriers are then collected, drained, depleted or recombined by a separate and faster mechanism. Electrical contacts are coupled to this full-featured region.
Tilted charge light emitters have many important applications in opto-electronics. It is among the objects hereof to devise techniques and devices for light-emitting transistors and transistor lasers that have new and improved characteristics and applications in opto-electronics.
SUMMARY OF THE INVENTIONIn accordance with a form of the invention, a ring cavity light-emitting transistor device is set forth, comprising: a planar semiconductor structure of a semiconductor base layer of a first conductivity type between semiconductor collector and emitter layers of a second conductivity type; base, collector, and emitter metalizations respectively coupled with said base layer, said collector layer, and said emitter layer, said base metallization comprising at least one annular ring coupled with a surface of said base layer; and an annular ring-shaped optical resonator in a region of said semiconductor structure generally including the interface of the base and emitter regions; whereby application of electrical signals with respect to said base, collector, and emitter metalizations causes light emission in said base layer that propagates in said ring-shaped optical resonator cavity. An embodiment of this form of the invention further comprises an electrical circuit for controlling application of said electrical signals with respect to said base, collector, and emitter metalizations to operate the device as either a light-emitting transistor or a transistor laser by controlling photon-assisted tunneling. The electrical circuit can comprise an optically controlled switch. In this embodiment, a quantum size region is provided within said semiconductor base layer. The quantum size region can comprise, for example, one or a plurality of quantum wells, quantum dot layers or quantum wire layers. Also in this embodiment, the semiconductor base layer is in the form of an annular mesa on the collector layer and the semiconductor emitter layer is in the form of an annular mesa on the base mesa, and the base and emitter metalizations are respectively deposited on the base and emitter mesas. Upper and lower optically reflective optical confinement regions, in the form of distributed Bragg reflectors, are provided for the ring-shaped optical resonator. Also, oxide confining rings are provided at the inner and outer sidewalls of the emitter mesa.
In accordance with another form of the invention, a method for optical switching, is set forth, including the following steps: providing a semiconductor device that includes a semiconductor base region of a first conductivity type between semiconductor collector and emitter regions of a second conductivity type, providing a quantum size region in said base region, and providing base, collector and emitter terminals respectively coupled with the base, collector, and emitter regions; providing electrical signals with respect to said base, collector, and emitter terminals to obtain light emission from said base region; providing an optical resonant cavity that encloses at least a portion of said base region; increasing the Q of said cavity to obtain substantially vertical collector-emitter voltage behavior as a function of collector current at a given base current; and switching between coherent and incoherent light emission from said base region by controlling said collector-emitter voltage to control photon-assisted tunneling. This technique can be implemented with edge-emitting and vertical-emitting devices. In a preferred embodiment of this form of the invention, the step of increasing the Q of the cavity comprises providing said optical resonant cavity as a continuous closed loop waveguide, such as a ring cavity.
In accordance with a further form of the invention, method is set forth for receiving an optical input signal and producing a switchable coherent optical output that depends on the optical input signal, including the following steps: providing a semiconductor device that includes a semiconductor base region of a first conductivity type between semiconductor collector and emitter regions of a second conductivity type, providing a quantum size region in the base region, and providing base, collector and emitter terminals respectively coupled with the base, collector, and emitter regions; providing electrical signals with respect to the base, collector, and emitter terminals to obtain light emission from the base region; providing an optical resonant cavity that encloses at least a portion of the base region; increasing the Q of said cavity to obtain substantially vertical collector-emitter voltage behavior as a function of collector current at a given base current; and providing an electo-optic circuit that is responsive to said optical input signal to substantially reduce or increase the collector-emitter voltage and switch the optical emission between coherent and incoherent light. In an embodiment of this form of the invention, the step of providing said opto-electronic circuit comprises providing a photodetector responsive to said optical input signal for coupling a reduced voltage to the collector terminal to control photon-assisted tunneling. In this embodiment, the step of increasing the Q of said cavity comprises providing said optical resonant cavity as a ring cavity.
In still another form of the invention, a method is set forth for storing binary optical information, including the following steps: providing a ring cavity light-emitting transistor; operating said ring cavity light-emitting transistor at first and second related operating points of its hysteresis characteristic, said first operating point causing spontaneous light emission from the ring cavity light-emitting transistor, and said second operating point causing laser emission from the ring cavity light-emitting transistor; and writing binary information for storage into the ring cavity light-emitting transistor by controlling selection of said first or said second operating point. In an embodiment of this form of the invention, the step of operating the ring cavity light-emitting transistor at first and second related operating points of its hysteresis characteristic comprises operating, for a particular base current, at a first operating point of a given collector current and a first collector-emitter voltage and a second operating point of the same given collector current and a second collector-emitter voltage. Also in this embodiment, the step of writing binary information comprises applying an optical pulse to an electro-optic circuit that is responsive to said optical pulse for controlling said collector-emitter voltage. This embodiment also includes the step of providing an optical erase signal to a further electro-optic circuit that is responsive to said erase signal to reset the collector-emitter voltage to a particular one of said first or second operating points.
Further features and advantages of the invention will become more readily apparent from the following detailed description when taken in conjunction with the accompanying drawings.
In order to show in full contrast the change in the TL operational range, the unaltered cleaved-cavity TL I-V characteristics of the earlier device are shown, repeated in the upper panel (A) of
The diagrams of
An example of a type of transistor laser crystal structure employed in our earlier work and preliminary hereto, can be realized using techniques previously reported (see M. Feng, N. Holonyak, Jr., G. Walter, and R. Chan, Appl. Phys. Lett. 87, 131103 (2005); M. Feng, N. Holonyak, Jr. R. Chan, A. James, and G. Walter, Appl. Phys. Lett. 88. 063509 (2006); and R. Chan, M. Feng, N. Holonyak, Jr., A. James, and G. Walter, Appl. Phys. Lett. 88, 143508 (2006)). For this example, from the substrate upwards, the epitaxial layers of the heterojunction bipolar transistor laser (HBTL) includes a 3000 Angstrom n-type heavily doped GaAs buffer layer, a 634 Angstrom n-type Al0.40Ga0.60As layer, a 5000 Angstrom n-type Al0.95Ga0.05As layer, and a 200 Angstrom n-type Al0.40Ga0.65As layer, followed by a 200 Angstrom n-type collector contact layer, a 120 Angstrom n-type In0.49Ga0.51P etch stop layer, a 600 Angstrom undoped GaAs collector layer, and then a 1010 Angstrom p-type GaAs base layer containing a 190 Angstrom undoped InGaAs quantum well (QW) designed for emission at λ≈1000 nm. On top is a 150 Angstrom n-type In0.49Ga0.51P emitter layer, a 150 Angstrom n-type Al0.35Ga0.65As layer, a 150 Angstrom n-type Al0.80Ga0.20As oxidation buffer layer, and a 4000 Angstrom n-type Al0.95Ga0.05As edge-oxidizable layer (to constrain emitter width), a 300 Angstrom n-type Al0.80Ga0.20As oxidation buffer layer, and a 500 Angstrom n-type Al0.35Ga0.65As layer. The HBLT laser structure is capped with a 1000 Angstrom heavily doped n-type GaAs contact layer.
The crystal processing into TL's can be accomplished basically as described in the above citations using SIN4 and photolithographic masking and patterning, standard wet etching of mesas and contact steps, and the usual contact metallization to effect the various stripe and contact geometries. Stripe emitter widths of 4, 6, and 8 μm on 500 μm centers (for convenient device separation) were used, as well as basic emitter lengths of ˜400 μm to allow mirror cleaving at 400 μm multiples. The basic stripe-geometry transistor laser TL, polished to a final thickness of ˜75 μm is heat sunk on In-coated Cu heat sinks, contacted with microwave-capable probes, and operated and tested.
The top panel (A) of
Spectra were taken from the unaltered facet and are shown in
As further described in APL 88, 232105, further enhancement of the cavity Q by increasing the second mirror reflecting (second deformable InGa ball) leads to further threshold reduction and further extension of the TL operational range, but it blocks the optical signal, making it necessary to use the data of
The TL threshold boundary along the lower and right edge of the shaded region of
A further edge emitting transistor laser, with similar layer structure was implemented with effectively increased Q, and exhibited sharp vertical collector current behavior at low temperature that is highly useful for opto-electronic switching.
The diagrams of
In accordance with an embodiment of the invention, a ring light-emitting transistor and ring transistor laser are set forth. (It will be understood that the reference to a ring designates a continuous loop that is preferably, but not necessarily, circular.) The ring cavity of a transistor laser (or light-emitting transistor) can have substantially less optical loss than conventional mirror-enclosed cavities and therefore can have a substantially higher Q. As a result of this and other attributes, operational advantages accrue, as further described herein.
Referring to
The simplified layer structure of the
Referring further to
The table of
An example of the present embodiment was fabricated with the following representative approximate dimensions: emitter ring width: 5 um, outer diameter of the ring d=50 urn, outer ring length=πd=157 um, oxidation depth: 0.5 um for each side (ring cavity is 4 urn). Base metal to emitter mesa distance is 2 um (both sides).
Referring to
Referring to
The graph of
In normal operation, with the photodetectors PD1 and PD2 non-conductive, the collector voltage is at VDD1 and, as seen in
The invention has been described with reference to particular preferred embodiments, but variations within the spirit and scope of the claimed invention will occur to those skilled in the art. For example, various principles hereof have application to vertical cavity lasers as well as to edge emitting lasers and to disk lasers that function to exhibit mirror gain.
Claims
1. A ring cavity light-emitting transistor device, comprising:
- a planar semiconductor structure of a semiconductor base layer of a first conductivity type between semiconductor collector and emitter layers of a second conductivity type;
- base, collector, and emitter metalizations respectively coupled with said base layer, said collector layer, and said emitter layer, said base metallization comprising at least one annular ring coupled with a surface of said base layer; and
- an annular ring-shaped optical resonator in a region of said semiconductor structure generally including the interface of the base and emitter layers;
- whereby application of electrical signals with respect to said base, collector, and emitter metalizations causes light emission in said base layer that propagates in said ring-shaped optical resonator cavity.
2. The device as defined by claim 1, further comprising an electrical circuit for controlling application of said electrical signals with respect to said base, collector, and emitter metalizations to operate said device as either a light-emitting transistor or a transistor laser, by controlling photon-assisted tunneling.
3. The device as defined by claim 2, wherein said electrical circuit comprises an optically controlled switch.
4. The device as defined by claim 2, further comprising a quantum size region within said semiconductor base layer.
5. The device as defined by claim 2, wherein said base metalization comprising at least one annular ring comprises two spaced apart concentric annular rings.
6. The device as defined by claim 2, wherein said emitter metalization comprises an annular ring concentric with said base metalization.
7. The device as defined by claim 6, wherein said collector metalization comprises a central disc concentric with said base metalization.
8. The device as defined by claim 2, wherein said semiconductor base layer is in the form of an annular mesa on said collector layer and said semiconductor emitter layer is in the form of an annular mesa on said base mesa, and wherein said base and emitter metalizations are respectively deposited on said base and emitter mesas.
9. The device as defined by claim 2, further comprising upper and lower optically reflective optical confinement regions for said ring-shaped optical resonator.
10. A method for optical switching, comprising the steps of:
- providing a semiconductor device that includes a semiconductor base region of a first conductivity type between semiconductor collector and emitter regions of a second conductivity type, providing a quantum size region in said base region, and providing base, collector and emitter terminals respectively coupled with said base, collector, and emitter regions;
- providing electrical signals with respect to said base, collector, and emitter terminals to obtain light emission from said base region;
- providing an optical resonant cavity that encloses at least a portion of said base region;
- increasing the Q of said cavity to obtain substantially vertical collector-emitter voltage behavior as a function of collector current at a given base current; and
- switching between coherent and incoherent light emission from said base region by controlling said collector-emitter voltage to control photon-assisted tunneling.
11. The method as defined by claim 10, wherein said step of increasing the Q of said cavity comprises providing said optical resonant cavity as a continuous closed loop waveguide.
12. A method for receiving an optical input signal and producing a switchable coherent optical output that depends on said optical input signal, comprising the steps of:
- providing a semiconductor device that includes a semiconductor base region of a first conductivity type between semiconductor collector and emitter regions of a second conductivity type, providing a quantum size region in said base region, and providing base, collector and emitter terminals respectively coupled with said base, collector, and emitter regions;
- providing electrical signals with respect to said base, collector, and emitter terminals to obtain light emission from said base region;
- providing an optical resonant cavity that encloses at least a portion of said base region;
- increasing the Q of said cavity to obtain substantially vertical collector-emitter voltage behavior as a function of collector current at a given base current; and
- providing an electo-optic circuit that is responsive to said optical input signal to substantially reduce or increase the collector-emitter voltage and switch said optical emission between coherent and incoherent light.
13. The method as defined by claim 12, wherein said step of providing said opto-electronic circuit comprises providing a photodetector responsive to said optical input signal for coupling a reduced voltage to said collector terminal to control photon-assisted tunneling.
14. The method as defined by claim 12, wherein said step of providing said semiconductor base region includes providing a quantum size region in said base region.
15. The method as defined by claim 12, wherein said step of increasing the Q of said cavity comprises providing said optical resonant cavity as a ring cavity.
16. A method for storing binary optical information, comprising the steps of:
- providing a ring cavity light-emitting transistor;
- operating said ring cavity light-emitting transistor at first and second related operating points of its hysteresis characteristic, said first operating point causing spontaneous light emission from said ring cavity light-emitting transistor, and said second operating point causing laser emission from said ring cavity light-emitting transistor; and
- writing binary information for storage into said ring cavity light-emitting transistor by controlling selection of said first or said second operating point.
17. The method as defined by claim 16, wherein said step of operating said ring cavity light-emitting transistor at first and second related operating points of its hysteresis characteristic comprises operating, for a particular base current, at a first operating point of a given collector current and a first collector-emitter voltage and a second operating point of the same given collector current and a second collector-emitter voltage.
18. The method as defined by claim 16, wherein said step of providing a ring cavity light-emitting transistor comprises:
- providing a planar semiconductor structure of a semiconductor base layer of a first conductivity type between semiconductor collector and emitter layers of a second conductivity type;
- providing base, collector, and emitter metalizations respectively coupled with said base layer, said collector layer, and said emitter layer, said base metallization comprising at least one annular ring coupled with a surface of said base layer;
- providing an annular ring-shaped optical resonator in a region of said semiconductor structure generally including the interface of the base and emitter layers; and
- applying electrical signals with respect to said base, collector, and emitter metalizations causes light emission in said base layer that propagates in said ring-shaped optical resonator cavity.
19. The method as defined by claim 18, further comprising the step of controlling application of said electrical signals with respect to said base, collector, and emitter metalizations to operate said device as either a light-emitting transistor or a transistor laser by controlling photon-assisted tunneling.
20. A method for producing light emission, comprising the steps of:
- providing a planar semiconductor structure of a semiconductor base layer of a first conductivity type between semiconductor collector and emitter layers of a second conductivity type;
- providing base, collector, and emitter metalizations respectively coupled with said base layer, said collector layer, and said emitter layer, said base metallization comprising at least one annular ring coupled with a surface of said base layer;
- providing an annular ring-shaped optical resonator in a region of said semiconductor structure including the interface of the base and emitter layers; and
- applying electrical signals with respect to said base, collector, and emitter metalizations to cause light emission in said base layer that propagates in said ring-shaped optical resonator cavity.
21. The method as defined by claim 20, further comprising the steps of controlling application of said electrical signals with respect to said base, collector, and emitter metalizations to operate said device as either a light-emitting transistor or a transistor laser.
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Type: Grant
Filed: May 26, 2015
Date of Patent: Oct 25, 2016
Patent Publication Number: 20160020579
Assignee: The Board of Trustees of The University of Illinois (Urbana, IL)
Inventors: Milton Feng (Champaign, IL), Nick Holonyak, Jr. (Urbana, IL), Mong-Kai Wu (Champaign, IL)
Primary Examiner: Harry W Byrne
Application Number: 14/545,587
International Classification: G11C 11/34 (20060101); H01S 5/062 (20060101); H01S 5/10 (20060101); H01S 5/34 (20060101); G11C 13/04 (20060101); G11C 7/10 (20060101); H01L 29/08 (20060101); H01L 29/417 (20060101); H01L 29/737 (20060101); H01L 29/06 (20060101); H01L 33/00 (20100101); G11C 7/00 (20060101); G11C 11/42 (20060101); H01L 33/10 (20100101);